1. Field of the Invention
This invention relates to a data receiving method used in a powerline environment, and more particularly, to a data receiving method and apparatus for receiving data from predetermined clear zones of a powerline.
2. Description of the Prior Art
Data communications methods used in a powerline environment have been discussed in many prior articles. One major data communications method is disclosed in U.S. Pat. No. 4,200,862 to Campbell et al, issued on Apr. 29, 1980. This invention discloses a powerline data communications method which uses a number of pulses generated within a predetermined clear zone of a powerline to transmit a digital data. Each pulse comprises a number of carrier cycles and the number of carrier cycles contained in each pulse defining its logic value. For example, a pulse which contains 48 to 160 cycles is interpreted by a receiver as a logic 0 and a number greater than 160 is interpreted as a logic 1. The problem with this method is that if the powerline comprises some noises which are close to the carrier frequency, the noises may couple with the carrier signals and cause many data errors in the receiving end. Besides, periodic noises are constantly existed in a powerline environment. If the frequencies of some periodic noises are close to the carrier frequency, many carrier signals will be corrupted by these periodic noises and the transmission efficiency will drop dramatically. Such weakness makes this technique become noise dependent.